TYRE COMPRISING A PIEZOELECTRIC DEVICE

Abstract

The present invention relates to a vehicle tyre comprising a piezoelectric device, wherein the piezoelectric device comprises a layer of a piezoelectric polymer having first and second opposing sides, and a first and a second layer of conductive rubber provided adjacent to the first and second opposing sides of the layer of piezoelectric polymer.

Claims

1. A vehicle tyre comprising a piezoelectric device, characterised in that the piezoelectric device comprises a layer of a piezoelectric polymer having first and second opposing sides, and a first and a second layer of an electrically conductive rubber composition provided adjacent to the first and second opposing sides of the layer of piezoelectric polymer.

2. The tyre according to claim 1, wherein the piezoelectric polymer is selected from the group of polyvinyldiene fluoride (PVDF) polymer, polyvinylidene fluoride-trifluoroethylene (P(VDF-co-TrFE)) copolymer, poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-co-CTFE)) copolymer, polyamides, liquid crystal polymers, poly(p-xylylene), and mixtures of these polymers.

3. The tyre according to claim 1, wherein the electrically conductive rubber composition has a volume resistivity of or below 10.sup.7 Ω.Math.cm at a temperature of 20° C. (determined from DMA measurements according to ISO 6721-12, frequency 1-100 Hz, 0.25 MPa dynamic stress and 0.35 MPa static stress), or in a range of ≥10.sup.3 Ω.Math.cm to ≤10.sup.7 Ω.Math.cm at a temperature of 90° C. (determined from DMA measurements according to ISO 6721-12, frequency 100 Hz, 0.25 MPa dynamic stress and 0.35 MPa static stress).

4. The tyre according to claim 1, wherein the electrically conductive rubber composition comprises a diene rubber selected from the group of natural rubber (NR), isoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR) or a mixture thereof.

5. The tyre according to claim 1, wherein the electrically conductive rubber composition comprises a conductive component selected from the group of carbon black, single-wall carbon nanotubes or multi-wall carbon nanotubes, graphene or a mixture thereof.

6. The tyre according to claim 1, wherein the electrically conductive rubber composition comprises single-wall carbon nanotubes in a range of ≥0.01 wt % to ≤2 wt %, preferably a range of ≥0.1 wt % to ≤0.6 wt %, based on a total weight of 100 wt % of the conductive rubber composition.

7. The tyre according to claim 1, wherein the electrically conductive rubber composition comprises carbon black in a range of ≥1 phr to ≤150 phr, preferably a range of ≥50 phr to ≤80 phr.

8. The tyre according to claim 1, wherein the piezoelectric polymer layer has a thickness in a range of ≥0.02 mm to ≤0.25 mm, preferably of 0.1 mm.

9. The tyre according to claim 1, wherein the first and second layer of electrically conductive rubber composition have a thickness in a range of ≥0.1 mm to ≤4 mm, preferably of 2 mm.

10. The tyre according to claim 1, wherein an inner liner forms an interior surface of the tyre structure and the piezoelectric device is provided on the interior surface of the inner liner.

11. The tyre according to claim 1, wherein the piezoelectric device is attached to a treadwall portion and/or a sidewall portion of the inner liner.

12. The tyre according to claim 1, wherein at least the first or the second layer of electrically conductive rubber composition forms the inner liner of the tyre.

13. The tyre according to claim 1, wherein the piezoelectric device forms the inner liner of the tyre.

14. The tyre according to claim 1, wherein the tyre comprises a tyre pressure monitoring system (TMPS) sensor which is powered by the piezoelectric device.

Description

EXAMPLES

[0033] The invention will be further described with reference to the following examples and figures without wishing to be limited by them.

[0034] FIG. 1 shows the output power of the temperature sweep from the sandwich-like piezoelectric devices including a PVDF film and elastomeric materials comprising carbon black and SWCNTs in different ratios.

[0035] FIG. 2 shows the output power of the frequency sweep from the sandwich-like piezoelectric devices including a PVDF film and elastomeric materials comprising carbon black and SWCNTs in different ratios.

[0036] FIG. 3 shows the output power of the frequency sweep and the temperature sweep from the sandwich-like piezoelectric devices including a PVDF film and elastomeric materials comprising carbon black and 6% wt SWCNTs in FIG. 3a) and in FIG. 3b), respectively.

EXAMPLE 1: PREPARATION OF A PIEZOELECTRIC DEVICE

[0037] A piezoelectric device of sandwich configuration with a 0.1 mm piezoelectric polymer layer of PVDF film configured in between two sheets of 2.0 mm conductive rubber, resulting in a piezoelectric patch of about 4.1 mm thickness, was prepared.

[0038] 1.1 Preparation of Piezoelectric Polymer Layer

[0039] The piezoelectric polymer PVDF was supplied from PolyK Technologies LLC, USA, in a form of thin film with A4 in size and a thickness of 100 m. The PVDF surface was cleaned by chloroform (99.5%, Sigma-Aldrich, St. Louis, Mo.) before treatment with oxygen plasma. The cleaned PVDF film was treated with an oxygen plasma treatment using a Plasma-Prep II (SPI Supplies, West Chester, USA) that contains a plasma vacuum chamber, in which the PVDF film was placed. At around 100-200 mTorr oxygen gas was pumped into the chamber and RF power at 13.56 MHz was applied to the chamber to excite and charge the oxygen molecules and create the oxygen plasma radicals. The PVDF film was continually treated for 15 minutes at room temperature (20±5° C.).

[0040] After oxygen treatment the PVDF was silanized with a thiocyanate based silane, namely 3-thiocyanatopropyltriethoxysilane (Si-264, Evonik Industries AG, Germany). For the silanization procedure, the PVDF film was exposed to 3 ml of silane S-264 in a desiccator under a vacuum atmosphere at room temperature for 24 hours.

[0041] 1.2 Preparation of Conductive Rubber Layer

[0042] Non vulcanized rubber sheets of conductive rubber compositions C.sub.ref, C.sub.1, C.sub.2 and C.sub.3, were prepared according to the table 1 below:

TABLE-US-00001 TABLE 1 C.sub.ref C.sub.1 C.sub.2 C.sub.3 amount amount amount amount Component: (phr) (phr) (phr) (phr) NR 25 25 25 25 SBR 25 25 25 25 BR 50 50 50 50 Filler 60 60 60 60 Processing oil 14 14 14 14 Curing agent 10 10 10 10 Anti Degradation agent 7 7 7 7 SWCNT/TDAE (10 wt % 0 4 8 12 SWCNT in TDAE)

[0043] The NR rubber used was TSR 20 grade.

[0044] The SBR rubber used was SBR 1502.

[0045] The BR rubber used was a Ni catalyzed Butadiene Rubber.

[0046] The filler used was carbon black N 330.

[0047] Abbreviations used are: TDAE (treated distillate aromatic extract; processing oil); SWCNT (Single Wall Carbon Nanotubes.

[0048] The mixture denoted C.sub.ref comprised carbon black as conductive component. In the three samples denoted C.sub.1, C.sub.2 and C.sub.3, respectively, 2, 4 and 6 wt % (given as 4, 8 and 12 phr, respectively) of a paste of highly conductive nano-fillers comprising 10 wt % of Single Wall Carbon Nanotubes (SWCNT) in a low aromatic plasticizer (TDAE) was added to the mixture C.sub.ref via a two roll-mill to improve conductivity. For good dispersion of the nano-fillers, the compound was passed and rolled the mills for ten times.

[0049] 1.3 Preparation of Piezoelectric Device

[0050] To prepare piezoelectric devices, the silanized PVDF film of step 1.1 was cured together with the layers of conductive rubber compound of step 1.2. The piezoelectric patches were fabricated in a sandwich configuration with a 0.1 mm thick PVDF film inserted in between two sheets of conductive rubber compounds comprising carbon black denoted of C.sub.ref, and further carbon nanotubes comprising C.sub.1, C.sub.2 and C.sub.3, respectively, and cured. The resulting cylindrical specimen had a sandwich-like configuration with a diameter of 10 mm and a thickness of 4.1 mm. In this configuration, the PVDF had a thickness of 0.1 mm, and the conductive material 2 mm thickness on the upper and lower side of PVDF. In the following, the resulting piezoelectric devices are denoted C.sub.ref, C.sub.1, C.sub.2 and C.sub.3 according to the respective conductive compounds.

EXAMPLE 2: DETERMINATION OF THE POWER OUTPUT OF THE PIEZOELECTRIC DEVICES VS. TEMPERATURE

[0051] The DMA (Dynamic Mechanical Analysis) technique is commonly used to analyse viscoelastic behaviours of polymeric materials by measuring stresses as a function of dynamic strains applied to the sample. Storage modulus, loss modulus and tan 6 of the sample can be determined under variable parameters, i.e. temperatures, frequencies and strains. These analysing parameters are important to simulate the dynamic mechanical conditions of a particular rubber product, e.g. tyres. The voltage was measured under dynamic mechanical conditions simulated by a DMA in order to measure the piezoelectricity of the materials.

[0052] Temperature sweep in DMA performed in compression mode was used to monitor the viscoelastic behaviour and the generated energy of the piezoelectric energy harvesters C.sub.ref, C.sub.1, C.sub.2 and C.sub.3 obtained in example 1.3 under dynamic deformation. DMA temperature sweep was carried out according to ISO 6721-12 on a DMA Eplexor 9 (Netzsch Gabo Instruments GmbH, Germany) in compression mode using a Voltage Module NI. Copper plates with electrical wires were attached to the upper and lower part of the specimen in order to create a connection with electrical detection devices. For compression mode, the cylindrical specimen were placed in between the compression sample holders and subjected to compressive forces by an oscillating upper plate of the sample holders. The temperature test was carried out by varying the temperatures in a range of 0 to 100° C. at 100 Hz. With this setup, the voltage output (V) of the specimens over a shunt resistor with a load of 4.7 MΩ were monitored, to calculate the output power using a Ohm's law.

[0053] The FIG. 1 shows the power outputs of the sandwich-like piezoelectric devices denoted C.sub.ref, C.sub.1, C.sub.2 and C.sub.3, in the temperature range of 0 to 100° C. As can be taken from the FIG. 1, by increasing analysis temperatures, the electricity was remarkably increased. It is assumed that this is because elevated temperatures accelerate electrical interactions. Thus, the conductivity of the electrical conductive compound is better at higher temperatures, resulting in an increased electrical intensity generated. Further it can be seen that the piezoelectric patch with the conductive compound including 0.6 wt % of carbon nanotube provided the highest electricity generation at 100° C., which is the operating temperature inside a tyre during its rolling.

EXAMPLE 3: DETERMINATION OF THE POWER OUTPUT OF THE PIEZOELECTRIC DEVICES VS. FREQUENCY

[0054] As a further analysis DMA frequency sweep was performed to monitor the viscolestic behaviour and the generated energy of the piezoelectric energy harvesters C.sub.ref, C.sub.1, C.sub.2 and C.sub.3 obtained in example 1.3 under dynamic deformation. DMA frequency sweep was carried out according to ISO 6721-12 on a DMA Eplexor 9 (Netzsch Gabo Instruments GmbH, Germany) in compression mode using a Voltage Module NI as described in example 2. For compression mode, the cylindrical specimen C.sub.ref, C.sub.1, C.sub.2 and C.sub.3 were placed in between the compression sample holders and subjected to compressive forces by an oscillating upper plate of the sample holders. The frequency test was carried out by varying the frequency in a range of 1-100 Hz at 20° C.

[0055] The FIG. 2 shows the output powers derived from the four sandwich-like piezoelectric devices denoted C.sub.ref, C.sub.1, C.sub.2 and C.sub.3, measured using a frequency range of 1 and 100 Hz. As can be taken from the FIG. 2, the power outputs of all samples increased with increasing frequency. Further it can be seen that the conductive compounds comprising carbon nanotubes showed an improved piezoelectricity compared to the device comprising only carbon black. Adding 6 wt % of the SWCNT/TDAE paste (10 wt % SWCNT in TDAE) showed the highest value of piezoelectricity.

[0056] This shows that the piezoelectric patch with the conductive compound including 0.6 wt % of carbon nanotube provided the highest electricity generation at 100 Hz, which is the vibration at which a piezoelectric device is subjected during the rolling tyre.

EXAMPLE 4: ESTIMATION OF THE POWER OUTPUT OF THE PIEZOELECTRIC DEVICE IN A CAR

[0057] The investigations of piezoelectric compounds of examples 2 and 3 reveal that it is highly promising to implement a piezoelectric system into a prototype tyre. The piezoelectric harvester was designed to have a sandwich-like configuration prepared from a piezo-polymer film with 0.1 mm thickness inserting in between the two layers of a conductive compound with 2 mm thickness. The output from the electrical harvester is in an alternating current (AC) waveform and has to be converted into a direct current (DC) signal by a rectifier, generating an effective current to the system. The generated electricity can be stored in a capacitor or a chargeable battery that can continually power the TPMS device installed in a tyre.

[0058] For the piezoelectric prototype the piezoelectric energy harvester C.sub.3 obtained in example 1.3 was selected as this device provided the best properties in examples 2 and 3. The piezoelectric sandwich C.sub.3 was glued with an amino-silicon sealant on the inner liner of treadwall inside a tyre.

[0059] A specific car was chosen as a reference to evaluate the efficiency of the piezoelectric sandwich. The reference car selected was a Volkswagen car, Golf series, with a total weight of 2100 kg, employing the tyres in P205/55R16 94R series. Under an assumption that the car is running at 80 km/h on average. With this driving condition, the revolution frequency is 11 Hz, and the estimated frequency due to tyre-road interactions is about 110 Hz. Moreover, the internal temperature of a rolling tyre can be built up from 80 to 100° C., depending on the weather or seasons.

[0060] For estimating the power output from the piezoelectric harvester, the analysing conditions with some assumptions were considered at a frequency of 100 Hz and a temperature of 90° C.

[0061] The FIG. 3 shows the output power generated by the piezoelectric sandwich patch C.sub.3 analysed under the frequency sweep at 20° C. in FIG. 3 a) and a temperature sweep at 100 Hz. These values were used for a calculation linking with the actual rolling conditions of the reference tyre.

[0062] As can be taken from the FIG. 3, at 100 Hz and 90° C. dynamic analyses, the output power from the piezoelectric patch C.sub.3 produces 28 μW/cm.sup.2. This shows that a sufficient amount of energy can be supplied to a TPMS sensor that needs 28 mW, when the piezoelectric patch C.sub.3 has a surface area of 0.1 m.sup.2, which can be installed inside the tyre, which is about 31.6×31.6 cm. This piezoelectric patch will generate electricity in a periodic manner by each revolution of the rolling tyre at the contact patch area, and the periodically generated electricity can be stored in a capacitor of the TPMS to ensure sufficient continual power supply to the system.